The present invention relates to resilient seals in turbines and particularly to methods of compressing a seal and retaining the compressed seal in a restrained condition as well as to methods for installing and releasing the seal in situ to seal against adjacent turbine parts.
In a gas turbine, hot gases of combustion flow from combustors through nozzles and buckets of the various turbine stages. Compressor discharge air is typically used to cool certain of the turbine elements. It will be appreciated that there is a need for seals at various locations in the turbine, as well as different types of seals. In co-pending U.S. patent application Ser. No. 10/028,928, filed Dec. 28, 2001 (Attorney Docket No. 839-1127) and Ser. No. 10/029,003, filed Dec. 28, 2001 (Attorney Docket No. 839-1124), there is disclosed a similar seal for use at two different locations within the turbine. For example, one of the disclosed seals may be used for sealing between the nozzle segments and a nozzle support ring to provide a seal supplemental to the chordal hinge seals sealing against leakage flow from the high pressure compressor discharge region into the lower pressure hot gas path. Another similar seal may be utilized for sealing between the nozzle retaining ring and shroud segments. Leakage paths or gaps sometimes appear between these sealing systems during turbine operations. In these and other sealing sites in a turbine, it is therefore desirable that seals be deployed between these sealing surfaces. Seal installation between these close-fitting sealing surfaces is difficult and it has been found desirable to compress the seals prior to and during installation to avoid damage to the seals and/or ancillary structure. Accordingly, there is a need for a seal which can be restrained in a compressed condition prior to and during installation and forms an effective seal under turbine operation conditions as well as for methods of installing and relieving the restrained seal for use.
In accordance with a preferred embodiment of the present invention, there is provided a resilient seal having sealing portions laterally spaced from one another and restrained in reduced lateral dimension prior to and during installation of the seal into the turbine. Subsequent to closure of the seal within sealing surfaces of the turbine parts, an operating condition of the turbine relieves or releases the restrained (compressed) seal, enabling the sealing surfaces to resiliently engage the adjacent sealing surfaces of the turbine parts to form the seal. In a particular preferred embodiment, the seal includes an elongated seal body having a generally U-shaped body portion in cross-section and a pair of reversely extending, generally U-shaped marginal portions in cross-section along opposite sides and at distal ends of the U-shaped body portion. In a preferred form, the seal is formed of sheet metal, preferably a pair of complementary-shaped sheet metal plates secured to one another in back-to-back relation and formed into the aforementioned configuration. Prior to installation, the seal is placed in a resiliently compressed or restrained state and maintained in that compressed state during installation. That is, the lateral sealing surfaces of the seal body are displaced toward one another and resiliently restrained in that condition prior to installation of the seal into the turbine to reduce the lateral extent of the seal. In that manner, the seal can be installed into a seal cavity on one of the turbine parts without any portion of the seal projecting from the seal cavity, enabling the assembly of the turbine parts without interference between the seal and the turbine parts.
To compress and maintain the seal in a compressed condition in accordance with a preferred embodiment hereof, the seal body is passed longitudinally between a pair of laterally spaced side-by-side rollers. The rollers displace the seal portions, e.g., the U-shaped marginal portions, toward one another to reduce the lateral extent of the seal. The compressed seal is then passed through a rotating bobbin holder ring which mounts a bobbin on its periphery for rotation about the elongated seal. As the compressed seal passes through the rotating bobbin holder ring, the fiber from the bobbin is wrapped about the compressed seal, maintaining the seal in its compressed condition. The bobbin holder ring may be alternately rotated about the seal in opposite directions to provide alternate clockwise and counterclockwise wrapping of the fiber about the seal. By wrapping the fiber in opposite directions, torsional effects on the seal due to the compressed wrapping are nullified.
The fibers are preferably formed of a material which will disintegrate at a turbine operating condition. Specifically, the fibers may be formed of carbon or a Kevlar(copyright) material known as Kevlar(copyright) 29. These carbon or Kevlar(copyright) fibers will disintegrate as the turbine heats up, releasing the seal from its compressed installation condition to an operable condition with the marginal sealing surfaces expanding to engage against sealing surfaces of the turbine parts, forming an effective seal. Preferably, the wrapped seal may be adhesively secured within the seal cavity to ensure that it resides completely within the cavity and does not fall out of the cavity during installation. At or below turbine operating temperatures, the epoxy and restraining fibers burn up and release the seal without leaving significant residue.
In a preferred embodiment according to the present invention, there is provided in a turbine having parts including a pair of adjacent surfaces and a flexible seal in sealing engagement with the adjacent surfaces, the seal having a pair of sealing portions preloaded to sealingly engage the pair of adjacent surfaces, respectively, upon installation of the seal into the turbine, a method of installing the flexible seal in the turbine, comprising the steps of locating the seal between the adjacent surfaces, maintaining the seal between the adjacent surfaces with the sealing portions thereof in a first position poised and biased for movement into sealing engagement with the adjacent surfaces and releasing the sealing portions of the seal in situ for movement from the first position into a second position in sealing engagement with the respective adjacent surfaces in response to a turbine operating condition.
In a further preferred embodiment according to the present invention, there is provided for a turbine having parts including a pair of adjacent surfaces and a flexible seal for sealing between the adjacent surfaces, the seal having a generally U-shaped body portion and a pair of sealing surfaces laterally spaced from one another along opposite sides of the U-shaped body portion, a method of forming the flexible seal for installation of the seal in the turbine, comprising the steps of resiliently displacing the sealing surfaces of the seal toward one another in a generally lateral direction into a turbine installation condition to reduce lateral spacing between the sealing surfaces relative to one another and preload the sealing surfaces for movement away from one another into a sealing condition, retaining the sealing surfaces in the installation condition while installing the seal between the pair of adjacent turbine surfaces and enabling the sealing surfaces for resilient movement away from one another into the sealing condition engaging and sealing against the adjacent surfaces of the turbine subsequent to closure of the sealing surfaces about the seal.